Thorp Air Command - T18.net

Guys, I need some advice. I recently found a crack in the hub of my A-D prop, so it's become a wall ornament. I've order a Catto 3 blade with a new spinner. I had a Landoll harmonic balancer installed with the old wood prop. Should I use it with the new prop or go without? One of the benefits of the 3 blade propeller is supposed to be that it is much smoother than a 2 blade prop. The new prop will weigh 3lbs. more than the old prop. Anyone have any experience with the harmonic balancer and a Catto 3 blade prop? I know I could just try it and see if i like it, but i thought I'd ask first.

Hi Scott,

Sorry to hear about your prop. I'm not a big fan of the harmonic dampeners (which is more correctly what that thing is), but to answer your question - it should work the same whether 2 or 3 blades.
Can you describe the crack (location, or pictures)? Was there excessive vibration? The bolts weren't torqued excessively causing deformation or crushing of the hub, were they? That's a real bummer.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Hi John,

The crack originated from the balance plug and radiated out toward the prop tip. It appears that there is a small gap between the plug filler and the hole wall that allowed the stress placed on the hub to create the crack. The torque was correct; the hub face/finish is not crushed. You can feel the crack when you run your fingernail across it.

Scott,

Not sure my response really gets to the crux of your question, but thought I'd give you my opinion regarding the Catto 3 blade prop. First, I think you made a great choice and you will be very satisfied with your choice. Craig Catto, like Mike, I found to be very approachable and knowledgeable. The 3 blade Catto is indeed smooth and a nice performer....oh and looks sexy too. I think due to the unfortunate situation with Mike more Thorpies will look for other options to fill the void and discover the Catto and it's attributes. I too pondered the addition of a harmonic balancer, but with the 3 blade it wasn't needed. I also have a heavy nose as it is and didn't want to exacerbate the weight and balance and further. The prop does stop rather abruptly however once the mixture is closed, I suppose most wood prop drivers are already accustomed that.

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Chuck Kincer
Richmond, Me
575CK
KIWI

Thanks, Chuck. I've seen photo's of your plane and hoped you would respond. I think I may just let the w&b determine whether I re-install the dampener. I have the same cowling as you, as well. Did you use the Van's 13" spinner?

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Scott Hinton
Elizabeth City, NC
N78WG

I'm fairly confident it's a 13", I'd have to check. Also, for a few extra $ Craig will cut the spinner for you.

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Chuck Kincer
Richmond, Me
575CK
KIWI

The new look...

man, that looks sharp!

What's an rv spinner doing on a Thorp!?!? You should be ashamed Scott!

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Well, Craig said he could cut and paint the spinner (he has them in stock). I kicked myself afterwards for not buying one of your carbon fiber spinners and having sent to him. I was in a rush to make Gary's fly-in. It looks good, but you're right, the Thorp spinner does look better. I sure hope Walt understands...

Scott,

Looks great! what pitch and diameter did you get? I'd be interested in performance numbers once you have them for comparison. Mine is a 66 x 70.

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Chuck Kincer
Richmond, Me
575CK
KIWI

Chuck,

It's a 68 X 70. I seem to have lost about 100 rpm and 5 mph top end, but climb rate is still 2000 fpm at 110 mph. I need to fly more to nail down reliable numbers. The prop is noticeably smoother and quieter and because I removed the harmonic dampener, the weight change was a net loss of 6 lbs. Plus, it looks cool!

Great look Scott!!.....though I think I would have made the black half of the spinner white, and the white half black. But that's just me.

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Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

It would be reversed if we were in the southern hemisphere, but since were not, that the way is should be. Besides, when it spins it looks the same!